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Subject[PATCH] random: Use wait_event_freezable() in add_hwgenerator_randomness()
Date
Sebastian reports that after commit ff296293b353 ("random: Support freezable
kthreads in add_hwgenerator_randomness()") we can call might_sleep() when the
task state is TASK_INTERRUPTIBLE (state=1). This leads to the following warning.

do not call blocking ops when !TASK_RUNNING; state=1 set at [<00000000349d1489>] prepare_to_wait_event+0x5a/0x180
WARNING: CPU: 0 PID: 828 at kernel/sched/core.c:6741 __might_sleep+0x6f/0x80
Modules linked in:

CPU: 0 PID: 828 Comm: hwrng Not tainted 5.3.0-rc7-next-20190903+ #46
RIP: 0010:__might_sleep+0x6f/0x80

Call Trace:
kthread_freezable_should_stop+0x1b/0x60
add_hwgenerator_randomness+0xdd/0x130
hwrng_fillfn+0xbf/0x120
kthread+0x10c/0x140
ret_from_fork+0x27/0x50

We shouldn't call kthread_freezable_should_stop() from deep within the
wait_event code because the task state is still set as
TASK_INTERRUPTIBLE instead of TASK_RUNNING and
kthread_freezable_should_stop() will try to call into the freezer with
the task in the wrong state. Use wait_event_freezable() instead so that
it calls schedule() in the right place and tries to enter the freezer
when the task state is TASK_RUNNING instead.

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Keerthy <j-keerthy@ti.com>
Fixes: ff296293b353 ("random: Support freezable kthreads in add_hwgenerator_randomness()")
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
---

See https://lkml.kernel.org/r/20190904110038.2bx25byitrejlteu@flow for
context on the bug report.

drivers/char/random.c | 12 +++++-------
1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 9b54cdb301d3..d3beed084c0a 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -327,6 +327,7 @@
#include <linux/percpu.h>
#include <linux/cryptohash.h>
#include <linux/fips.h>
+#include <linux/freezer.h>
#include <linux/ptrace.h>
#include <linux/workqueue.h>
#include <linux/irq.h>
@@ -2429,7 +2430,6 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
size_t entropy)
{
struct entropy_store *poolp = &input_pool;
- bool frozen = false;

if (unlikely(crng_init == 0)) {
crng_fast_load(buffer, count);
@@ -2440,13 +2440,11 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
* We'll be woken up again once below random_write_wakeup_thresh,
* or when the calling thread is about to terminate.
*/
- wait_event_interruptible(random_write_wait,
- kthread_freezable_should_stop(&frozen) ||
+ wait_event_freezable(random_write_wait,
+ kthread_should_stop() ||
ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits);
- if (!frozen) {
- mix_pool_bytes(poolp, buffer, count);
- credit_entropy_bits(poolp, entropy);
- }
+ mix_pool_bytes(poolp, buffer, count);
+ credit_entropy_bits(poolp, entropy);
}
EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);

--
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